Scientists in India have identified, for the first time, the precise ways in which two widely used preservatives attack and destroy bacteria. The breakthrough, a collaboration between the Institute of Nano Science and Technology (INST) Mohali, an autonomous institute of the Department of Science and Technology, and Unilever R&D Bangalore, shows how sodium benzoate and phenoxyethanol disable bacterial cells. The findings could allow manufacturers to formulate safer, more effective preservation systems for food and personal care products, and help prevent the development of bacterial resistance.
Key facts
- Research conducted at Institute of Nano Science and Technology (INST) Mohali, Department of Science and Technology
- Collaboration partner: Unilever R&D Bangalore
- Two preservatives studied: Sodium benzoate (used since 1908) and Phenoxyethanol (used for decades in personal care and vaccines)
- Bacteria tested: Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative)
- Sodium benzoate shows 16-fold increase in activity in acidic environments
- Phenoxyethanol shows consistent efficacy across varied pH ranges
- Published in Letters in Applied Microbiology (DOI: 10.1093/lambio/ovag022)
- Research team: Ishani Sharma, S M Rose, Madhu Lata, Somnath Das, Nagaraja IS Acharya, Maheshwara Naik, Samiran Mahapatra and Sharmistha Sinha
How preservatives attack bacteria
The research revealed that both preservatives do not work through a single mechanism. Instead, they launch a multi-pronged attack on bacterial cells. The preservatives compromise the physical structure of the bacterial cell envelope, the outer protective layer that keeps the bacterium intact. Simultaneously, they trigger internal biochemical damage by allowing reactive aldehydes and oxygen-derived compounds to accumulate inside the cell. This internal buildup disrupts essential proteins and genetic material, essentially crippling the bacteria from within.
The two preservatives, however, follow different pathways to achieve this outcome. Sodium benzoate causes the bacterial cell to shrink and eventually collapse, like a balloon deflating. Phenoxyethanol, by contrast, causes the cell membrane to expand abnormally before rupturing entirely. These visual differences, captured using transmission electron microscopy, show that the same end result can be achieved through distinct biological mechanisms.
Performance in different conditions
The study found important differences in how each preservative performs depending on the acidity of the environment. Sodium benzoate becomes significantly more powerful in acidic conditions, showing approximately 16 times greater activity than in neutral settings. This makes it ideal for preserving acidic foods such as pickles, ketchup and fizzy drinks, where it has been used since being approved by the US Food and Drug Administration in 1908.
Phenoxyethanol, used in shampoos, moisturisers, sunscreens and some vaccines, maintains consistent effectiveness across a wide range of pH conditions. This flexibility means it can be used in formulations where the acidity or alkalinity might vary or is difficult to control.
Research methods
The team employed multiple sophisticated techniques to observe preservatives in action. They used inhibition zone assays and minimum inhibitory concentration (MIC) tests to determine how much preservative was needed to stop bacterial growth. Transmission electron microscopy allowed them to watch the bacterial cell structure deteriorate in real time. Dye leakage tests revealed when bacterial membranes developed breaches. Two biochemical assays, MBTH and DCFDA, measured the accumulation of internal chemical damage. By combining these methods and testing against two very different types of bacteria in both neutral and acidic conditions, the researchers connected observable physical changes in the bacteria to the underlying biochemical chaos occurring inside the cells simultaneously.
What this means for industry and consumers
Understanding exactly how preservatives work allows manufacturers to make better choices. Industries can now select the most appropriate preservative for their specific product format rather than relying on guesswork. They can also use the minimum effective amount rather than over-preserving, reducing unnecessary chemical exposure. Better-formulated preservation systems mean less food spoilage and waste, translating to reduced costs and environmental benefits. Additionally, by understanding the multi-target mechanism of these preservatives, manufacturers can work to prevent bacteria from evolving resistance, a growing global health concern.